The present invention relates to a device and method for controlling an electromagnet controlling a metering valve of an internal combustion engine fuel injector.
As is known, a metering valve is normally opened by exciting an electromagnet controlling the valve. Excitation of the electromagnet commences at a given instant depending on the stroke of the corresponding engine cylinder, and is effected by a first current. After a given delay, sufficient to ensure the valve is opened completely, the first current is replaced by a second current, which is lower, e.g. about half, the first current, to simply keep the electromagnet excited and the valve open. The instant the second current ceases depends on the amount of fuel required by the engine, so that the total excitation time of the electromagnet depends on the operating conditions, e.g. speed, torque, etc., of the engine.
Owing to the hysteresis of the electromagnet core, which depends on the type of material used, the decay time of the magnetic field of the coil varies with time, so that the electromagnet is excited by a current whose time graph, as of the first instant, comprises a portion increasing rapidly to a substantially constant first current, a portion decreasing to a lower second current from another instant having a predetermined delay with respect to the first, and a portion in which the second current decreases to zero from a second instant.
In known control devices, the delay is selected to ensure the valve opens in any condition, in particular with any engine and fuel temperature, and is therefore fairly long. The transition in the excitation of the electromagnet, from the higher to the lower current, results in nonlinearity of the quantity of fuel injected as a function of excitation time. Moreover, in known devices and in certain engine operating conditions, nonlinearity frequently occurs at a critical point in the operation of the engine, thus resulting in irregular power output.
It is an object of the present invention to provide a device and method for controlling an electromagnet controlling a fuel injector metering valve, which are highly straightforward and reliable, and provide for eliminating the aforementioned drawbacks typically associated with known devices.
According to the present invention, there is provided a device for controlling an electromagnet controlling a metering valve of a fuel injector of an internal combustion engine, and which comprises an electric circuit for generating a first electric current of such a predetermined value as to excite said electromagnet to open said metering valve; said electric circuit generating a second electric current of a value lower than said predetermined value and such as to keep said electromagnet so excited; timing means being provided to control said electric circuit as a function of operating conditions of said engine; and the device being characterized in that said timing means also control said electric circuit in such a manner as to vary the duration of said first current as a function of the operating temperature of said engine.
According to the relative control method, the electromagnet is first excited by a first electric current of such a predetermined value as to open the metering valve, and is subsequently kept excited by a second electric current of a value lower than said predetermined value; the method being characterized by varying the duration of said first current as a function of the operating temperature of said engine.